2. What is Refractive Index?
The refractive index of a medium is defined as the ratio of
the velocity of light in a vacuum to the velocity of light in
the medium.
A ray of light travels more slowly in an optically dense
medium than in one that is less dense.
3. What is Refraction?
When a ray is incident on the interface between two
dielectrics of differing refractive indices (e.g. glass–air),
refraction occurs
4. As the angle
of incidence
Increases,
the angle of
refraction
Increases.
5. Watch the video clip
https://www.youtube.com/watch?v=T-iy29oEmSI
What is the difference between critical angle and total
angle of reflection??
6. What is Critical Angle?
•At a certain angle, the
refracted ray follows a
path exactly along the
surface of the dense
medium.
•When the angle of
refraction is at 90°
the incident angle is
called the “Critical
Angle”
7. What is Total Internal
Reflection (TIR)?
•If the incident ray is
increased beyond the
critical angle, the light is
no longer refracted
• Instead, it is reflected
back inside the
medium
• This is called “total
internal reflection”
10. Conditions for TIR & Critical
Angle
Light is travelling slower in the first medium than in the
second medium (v1 < v2)
Thus light is moving from medium of higher refractive index
to one of lower refractive index (n1 > n2)
Critical angle (C) is defined when the angle of refraction is
90° to the normal (θ2 = 90°)
TIR occurs when angle of incidence is larger than the critical
angle (θ1 > C)
12. Critical angles of different
materials
Medium
Refractive
Index
Critical
Angle
Glass 1.50–1.70 30°–42°
Water 1.33 49°
Perspex 1.5 42°
Diamond 2.42 24°
13. Applications of TIR
TIR in Fiber Optics
Communication
Endoscopes
TIR in Prism
Periscopes
Binoculars
Single Lens Camera
Retro Reflectors
14. Dispersion and the Rainbow
The index of refraction varies slightly
with the frequency of light; in general,
the higher the frequency, the higher the
index of refraction.
This means that
refracted light is
“spread out” in a
rainbow of colors;
this phenomenon
is known as
dispersion.
15. Dispersion and the Rainbow
Rainbows are created by the dispersion of light
as it refracts in a rain drop.
16. Dispersion and the Rainbow
As the drop falls, all the colors of the rainbow
arrive at the eye.
18. • Aberration occurs when the incident light fails to focus at a single
point.
• The aberration types are:
1. Monochromatic aberrations (can be produced with a single wavelength of
light):
• Spherical Aberration
• Coma
• Oblique Astigmatism
• Power Error (Field Curvature)
• Distortion
2. Chromatic aberration (occur only with polychromatic light).
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Aberration
19. Monochromatic
aberrations
• They called monochromatic aberrations, since they occur
independently of color.
• The 5 Seidel aberrations are spherical aberration, coma, oblique
astigmatism, curvature of field (power error), and distortion.
Peripheral rays
* Peripheral rays are those that enter the lens nearer the edge
of the lens.
* Paraxial rays are those that pass through the central area of
the lens.
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